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Improving SO 2 AMFs: Comparison of different approaches P. Hedelt , P. Valks , D. Loyola

Improving SO 2 AMFs: Comparison of different approaches P. Hedelt , P. Valks , D. Loyola Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR) Institut für Methodik der Fernerkundung Abteilung Atmosphärenprozesooren First German S5P Verification Meeting, Bremen 28-29. November 2013.

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Improving SO 2 AMFs: Comparison of different approaches P. Hedelt , P. Valks , D. Loyola

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  1. Improving SO2 AMFs:Comparisonof different approaches P. Hedelt, P. Valks, D. Loyola Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR) Institut für Methodik der Fernerkundung Abteilung Atmosphärenprozesooren First German S5P Verification Meeting, Bremen 28-29. November 2013

  2. Overview • Prototype Algorithm: • Fitting windows: • 312-326nm • 325-335nm (VCD>40 DU) • 360-390nm (VCD>250DU) • Single Wavelength AMF • VerificationAlgorithm: • Fitting windows • 312-324nm • 326.5-335nm (VCD>40 DU) • AMF: Different Approaches • The SO2amountandplumeheightisunknownatthe time ofthemeasurement • Directfittingcomputationaltoo expensive

  3. Currentaproach:Classical DOAS approach • Current GOME-2 SO2 approach • DOAS fit ofmeasuredspectra SO2 SCD • Single-wavelength AMF • Viewing & surface/cloudconditions • Fixed SO2profile (Gaussianat 2.5, 6 and 15km) • SO2 VCD assumedfor AMF: • Standard fittingwindow: 3 DU • VCDs underestimated > 25 DU! • VCD=SCD/AMF • Approach independentofmeasured SO2 SCD

  4. Currentaproach:Classical DOAS approach • Current GOME-2 SO2 approach • DOAS fit ofmeasuredspectra SO2 SCD • Single-wavelength AMF • Viewing & surface/cloudconditions • Fixed SO2profile (Gaussianat 2.5, 6 and 15km) • SO2 VCD assumedfor AMF: • Standard fittingwindow: 3 DU • VCDs underestimated > 25 DU! • Alternative fittingwindow (>40 DU): 100 DU • Currentlyunderinvestigation • VCD=SCD/AMF • Approach independentofmeasured SO2 SCD

  5. Improvedapproach:Iterative AMF approach • Approach based on GOME-2 O3retrieval • DOAS fit ofmeasuredspectra SO2 SCD • Single-wavelengthAMF • Viewing& surface/cloudconditions • Fixed SO2profile(Gaussianat 2.5, 6 and 15km) • Calculationof AMF in iterative way • Determine VCD frominitial (arbitrary) AMF • Calculatenew AMF • Iterateuntil VCD converges • VCD = SCD/AMF • AMF (partly) depends on measured SO2 SCD

  6. Improvedapproach:Empirical DOAS approach • Approach based on OMI O3 retrieval • DOAS fit ofmeasuredspectra SO2SCD • Creationofsimulatedspectra (312-335nm) • Viewing& surface/cloudconditions • Fixed SO2profile (2,5km FWHM Gaussianat 2.5, 6 and 15km) • Assumingsetof SO2 VCDs • DOAS fit ofsimulatedspectra SCDs forassumed VCDs • Interpolation ofmeasured SCD on retrieved SCD grid  SO2 VCD • VCD depends on measured SCD • Errors in DOAS fit cancel out

  7. ExamplesKasatochi 08-08-2008

  8. ExamplesKasatochi 09-08-2008

  9. ExamplesGrimsvötn 23-05-2011

  10. Current Status • Classical DOAS approach • (GOME-2) LUT readyfor Standard fittingwindow • S5P LUT canbecreatedvery fast • Iterative AMF approach • AMFs arecurrentlycalculated on-line • AMF LUTs for different VCDs canbecreatedfast • Empirical DOAS • (GOME-2) Spectrahavebeencomputedfrom 312-335nm • VCD LUT for different fittingwindowsisready • LUT interpolationunderconstruction • Currentlytestsareperformed • S5P spectragenerationtakeabout 1 month

  11. Physicalparametersof LUTs

  12. Summary & Conclusion • Currentapproach • AMF independentofmeasured SO2 SCD • VCDs areunder/overestimated • Iterative AMF approach • AMF isfitted in iterative way • AMF partlydependent on measured SCD • Better VCDs • Empirical DOAS approach • DOAS fit ofbothmeasured an simulatedspectra • AMF (or VCD) depends on measured SCD • DOAS errorspotentially cancel out • Resultsclosetodirectfittingresults

  13. Thankyouforyourattention!

  14. Summary • Classical DOAS approach: • Single-wavelengthAMF forviewing & surfaceconditions (315 / 327nm) • Independent ofmeasured SO2 SCD • Underestimateshigh SO2 VCDs • Iterative AMF approach • Single-wavelength AMF forviewing & surfaceconditions (315 / 327nm) • Iterative AMF fitting • AMF (partly) depends on SCD • Empirical DOAS approach • DOAS retrievalofsimulatedspectra on pre-defined VCD grid • Interpolation ofmeasured SCD on gridofsimulated SCDs • Dependent on measured SO2 SCD • Errors in DOAS fit cancel out

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